Characterization of copper species over Cu/SAPO-34 in selective catalytic reduction of NOx with ammonia: Relationships between active Cu sites and de-NOx performance at low temperature

To investigate the active Cu sites in the selective catalytic reduction of NO by NH3 (NH3 SCR) over Cu/SAPO-34 catalysts, a series of samples containing different Cu loadings has been prepared by an ion-exchange process. A combination of H2 TPR and EPR techniques was applied to identify and quantify the isolated Cu2+ sites. The trend of the isolated Cu2+ ions in the samples estimated by EPR is similar to that from TPR results and was found to be proportional to the NH3 SCR reaction rates. The turnover frequency (TOF) calculated based on the number of isolated Cu2+ ions on samples with varying Cu loadings showed a constant value at the same temperature. Thus, we conclude that the isolated Cu2+ species associated with the six-ring window and displaced into the ellipsoidal cavity of SAPO-34 (Site (I)) are the active sites for the NH3 SCR reaction in the temperature range 100–200 °C.